P8 forces in balance

8.1 vectors and scalars

• scaler only has magnitude (fancy word for size)

• vectors have magnitude and direction

• examples of scalar:

  • energy

  • mass

  • power

  • distance

  • speed

  • time

• examples of vector:

  • velocity

  • force

  • weight

  • displacement

  • momentum

8.2 forces between objects

• a force can change the shape of the object or it’s motion

• a contact force can only act on the object if it’s touching it

• third law of motion - when objects touch they exert equal and opposite forces on each other

  • for every action in nature there is an equal and opposite reaction

  • 

8.3 resultant forces

• the resultant force is a single force that combines the effect of all of the other forces together

  • if one of the forces is acting north the other west the resultant forces would be acting north west

• newtons first law of motion is that if the forces acting on it are equal then the resulting force is 0

  • this can mean the object is not moving

  • or moving at a consistent speed and the same direction

• if it’s more than 0 it will change direction or speed

• if two forces are acting along the same line their force is either the sum if its in the same direction or the difference if it’s acting in opposite

• a free body diagram is the forces acting on the object, but the arrows have to be proportional to the size of the force and drawn in the direction it is acting

  • 

8.4 moments at work

• the turning effect of the force is called a moment

• the size of the moment is M = F x d

  • M is the moment, in Nm (newton meters)

  • F is the force, in N

  • d is the perpendicular distance from the line of action of the force to the pivot, in m

  • 

8.5 more about levers and gears

• levers are used as force multipliers which means the force exerted is much greater than the force applied

• the pivot of the force multiplier is nearer to the force exerted than the force applied

• gears are used to change the moment of a turning affect

• 

• to increase the moment of the turning effect a small gear wheel needs to drive the big gear wheel

8.6 centre of mass

• if the object is symmetrical the centre of mass lies on the axis of symmetry

• the centre if mass is where the mass is the most concentrated

• if the object is freely suspended the centre of mass will be directly underneath the point it’s being hung from, it is at equilibrium

8.7 moments and equilibrium (???????????????????????????)

• if the object at rest doesn’t turn it means, the sum of anticlockwise moments at any point = the sum of clockwise moments at any point

• if the object is at equilibrium it is balanced, this means that at any point you can find the sum of clockwise and anticlockwise moments and find they are the same, this is called the principle of moments

8.8 parallelogram of forces (try on paper)

• finds the resultant force

8.9 resolution of forces (do on paper)

• i actually dunno

1. scaler - distance

   vector - displacement

2. a force that acts when two objects touch

3. M = Fd

   M = 35 x 2.1

   73.5

4. the centre of mass is at the axis of symmetry

5. a vector quality has magnitude and direction

6. third law - when objects touch there’s an equal and opposite force acting on it